1. Field of the Invention
The present invention relates to an apparatus and system for logging wells as they are drilled into a targeted geologic formation. More specifically, the present invention relates to an apparatus and a system for configuring a well logging tool with devices that generate and detect electromagnetic, acoustic, and other physical signals.
2. Background of the Related Art
Well logging devices are lowered into a drilled earthen bore to detect conditions in a geologic formation penetrated by the bore. The detected conditions generally indicate the presence and/or absence of certain fluids that reside in the pores of the rock that makes up the geologic formation. Well logging devices include devices that generate signals aimed at a geologic formation adjacent to the bore and devices that detect those signals that are reflected by or returned from the geologic formation. Some well logging devices include a first well logging device to induce an electrical current to flow within the geologic formation of interest and a second well logging device to measure the resulting current flow in the formation to determine the electrical resistivity of materials residing within the formation. A high resistance to current flow generally indicates that a non-conductive fluid, such as oil or gas, resides in the pores of the formation while a low resistance to current flow generally indicates that a conductive fluid, such as water, resides in the pores of the formation.
In some applications, the spacing of a first, signal-generating well logging device on a well logging tool relative to a second, signal-detecting well device instrument on the well logging tool determines the depth of investigation; that is, the spacing between the first and second well logging devices determines the distance into the formation and from the bore in which the tool is disposed that is being investigated using the well logging devices. A greater the separation of the first well logging device from the second well logging device provides a greater distance into the geologic formation from the tool that is investigated, and a lesser separation of the first well logging device from the second well logging device provides a lesser distance into the formation from the tool that is investigated.
It is advantageous to investigate the properties of the formation at varying distances from the bore in order to better determine and account for changes in the formation occurring as a result of near-bore exposure to pressurized drilling fluids and to better determine a weighted-average property of the formation based on a plurality of detected conditions.